An energy-restricted diet is often prescribed before bariatric surgery to reduce weight and liver volume. While very-low-calorie diets (VLCDs, 450-800 kcal per day) have shown to be effective, the effectiveness of low-calorie diets (LCDs, 800-1500 kcal per day) is less obvious. The objective of this systematic review was to elucidate the effectiveness of LCD on liver volume reduction in patients awaiting bariatric surgery. Eight studies (n = 251) were included describing nine different diets (800-1200 kcal, 2-8 weeks). An LCD was effective in liver volume reduction (12-27%) and weight loss (4-17%), particularly during the first weeks. The LCD showed an acceptable patients' compliance. Based on these findings, an LCD (800-1200 kcal), instead of a VLCD, for 2 to 4 weeks should be preferred.